This invention relates to needle bars for staggered needle tufting machines and more particularly to a staggered needle bar construction permitting longitudinal adjustment of one row of needles relative to the other to permit compensation for hook deflection in very fine gauge tufting machines.
It is known to use a staggered needle bar construction in a tufting machine to produce relatively dense pile tufted fabric. In such construction two parallel rows of needles are mounted transversely or laterally relative to the direction of feed of the backing material and the needles in one of the rows is offset or staggered relative to the needles in the other row. Thus, the needles in one row are disposed laterally half-way intermediate adjacent needles in the other row. Such a construction provides tufts at half the gauge of each row of needles. The staggered needle bar construction has been utilized for both loop pile tufting machines such as illustrated in Webb U.S. Pat. No. 3,492,956, and cut pile tufting machines such as illustrated in Crumbliss, et al U.S. Pat. No. 3,913,505.
When staggering the needles in the needle bar the loopers or hooks which cooperate with the respective needles must be of two types. One set of loopers or hooks have a short bill for cooperating with the needles in the front or rear row and the other set have a long bill for cooperating with the needles in the rear or front row, the disposition of rows being relative to the direction in which the base material is fed, so that loops of yarn presented by the needles are seized by all the loopers or hooks.
In cut pile tufting machines knives cooperate with the respective hooks and act against a face thereof to cut the yarn loops on the hooks. The knives are set against the hooks with sufficient pressure for effective cutting action to occur and deflect the hooks slightly. In machines that produce fine gauge fabrics, e.g. 5/64 inch spacing between longitudinal rows of stitches, and especially 1/16 inch and smaller, the hooks must be extremely thin and relatively substantial deflection results. In machines having a staggered needle bar the longer billed hook deflects further than the shorter billed hook. Conventionally, in staggered needle bar machines the needles in one row are fixed relative to the needles in the other row and no provision for the differential in deflection is possible. Thus, at the time the machine is assembled or when gauge parts are replaced, the positioning of one set of hooks to seize loops from their respective needles may result in the other set of hooks failing to seize loops from their respective needles on every stroke due to the greater deflection of the long billed hooks.